1. Field of the Invention
The present invention relates to a method for patterning a metal layer on an insulating substrate and, more particularly, to a metal layer patterning method which is suitable for use in forming interconnect layers of semiconductor integrated circuits or mask layers employed for the formation of such interconnect layers or the like in the fabrication of semiconductor integrated circuits.
2. Description of the Prior Art
The most common traditional way of forming an interconnect layer of a semiconductor integrated circuit by a metal layer as of aluminum, aluminum-silicon alloy, aluminum-copper alloy or copper and mask layer therefor by a metal layer as of chromium comprises the steps of forming on a semiconductor layer a metal layer to be patterned, forming a patterned mask layer of photoresost on the metal layer and carrying out chemical etching of the metal layer by an etchant through the mask layer for a predetermined period of time, thereby patterning the metal layer into the interconnect layer or mask layer desired to obtain.
With such a conventional method, however, during the abovesaid chemical etching the metal layer to be patterned is inevitably subjected to what is called side etching by an amount dependent upon the length of chemical etching, resulting in the patterned metal layer becoming smaller than the pattern of the mask layer by the amount of side etching.
It is desirable, of course, that the patterned metal layer be of the same pattern as that of the mask layer. The reason is that the metal layer can be obtained in a desired pattern only by forming the mask layer in the same pattern as that of the metal layer.
Even in the case where the metal layer is subjected to side etching in the aforementioned step of chemical etching, however, if the amount of side etching of the metal layer were predicatable, the metal layer could be obtained in the desired pattern by forming the mask layer in a pattern of a size larger than the predetermined pattern of the metal layer in anticipation of the amount of side etching predicted.
But, according to the aforesaid prior art method, since the amount of side etching depends upon the temperature, the flow rate and other conditions of the etchant used, it is very difficult to predict the amount of side etching.
Therefore, the aforementioned conventional method encounters difficulty in forming the metal layer in the desired pattern with good reproducibility and with high precision.